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NASA will begin the launch countdown for Space Shuttle Atlantis' STS-115 mission at 6 p.m. EDT Thursday, Aug. 24, at the T-43 hour point. During this mission, Atlantis' crew will resume construction of the International Space Station, which is the goal of the remaining space shuttle flights until the spacecraft are retired in 2010.

The NASA Kennedy Space Center launch team will conduct the countdown from the newly renovated firing room 4 of the Launch Control Center. The countdown includes 27 hours, 24 minutes of built-in hold time leading to a preferred launch time at about 4:30 p.m. on Sunday, Aug. 27. The launch window for that day extends an additional five minutes.

This mission is the 116th space shuttle flight, the 27th flight for Atlantis and the 19th U.S. flight to the International Space Station. STS-115 is scheduled to last 11 days with a landing at Kennedy about 12:02 p.m. EDT on Sept. 7.

Atlantis' last mission was STS-112 in October 2002. In preparation for STS-115, Atlantis was moved into Kennedy's Vehicle Assembly Building on July 24. Atlantis then was attached to its modified external tank and solid rocket boosters. Space Shuttle Atlantis was rolled out to Launch Pad 39B on Aug. 2.

During STS-115, Atlantis' astronauts will deliver and install the 17.5-ton, bus-sized P3/P4 integrated truss segment on the station. The girder-like truss includes a set of giant solar arrays, batteries and associated electronics. The P3/P4 truss segment will provide one-fourth of the total power-generation capability for the completed station.

For information about the STS-115 crew and its mission to the International Space Station, visit:

Final preparations of the shuttle's three main engines for main propellant tanking (2 a.m.) Begin filling pad sound suppression system water tank (4 a.m.) Pad sound suppression system water tank filling complete (7 a.m.) Close out the tail service masts on the mobile launcher platform Begin star tracker functional checks (9:50 a.m.)